Thermal ribbon cartridge or roll with slack ribbon retraction

FIELD OF THE INVENTION

00002The present invention relates to thermal transfer printers and more specifically to a ribbon cartridge or roll for a thermal transfer printer, which automatically retracts ribbon slack resulting from backfeed.

BACKGROUND OF THE INVENTION

00003Thermal transfer printers are well known in the art. In such printers, a transfer ribbon coated on one side with a heat-transferable ink layer is interposed between the surface of a non-sensitized web and a thermal print head having a line of small heater elements. When an electrical signal or pulse is applied to a selected subset of the heater elements, localized melting and transfer of the ink to the web occurs, resulting in a corresponding line of dots being transferred. The web is then advanced to print an adjacent location, and the transfer ribbon is repositioned to provide a replenished ink coating. The selecting and heating process is repeated to print an adjacent line of dots. Patterns of successive dots produce printed text or graphics on the web.

00004Thermal transfer printers are particularly well suited to printing a web of individual tags, tickets, and labels. In such printers, the web is advanced past the print head so the trailing edge of a tag, ticket, or label extends beyond a mechanical cutter or tear-off edge. To reduce waste, it is preferable to backfeed the web before printing again. This results in a corresponding backfeed of the transfer ribbon and the potential for slack ribbon. If slack ribbon is allowed to remain, the resulting loss of ribbon tension may cause the ribbon to wrinkle upon advance, with a resulting loss of print quality. To prevent this, known thermal label ticket and tag printers are typically equipped with a spindle for the ribbon supply roll having a torsion spring and clutch. Forward advancement of the ribbon winds the spring until the spring force overcomes the clutch force, at which point the ribbon feeds at a desired tension determined by the clutch torque.

00005If a thermal transfer printer according to the prior art must further be capable of printing a range of label, ticket, or tag widths, then the ribbon tension will vary with ribbon width, and no single setting of clutch torque may suffice. The ribbon may wrinkle if the tension is set too low to accommodate a narrower ribbon than is being used, and it may slip if it is set too high to accommodate a wider ribbon than is being used. To address this, the ribbon supply spindle may be equipped with user or technician adjustment for spindle torque. Alternatively, the ribbon supply spindle can be segmented and may have a separate spring and clutch for each segment, such that wider ribbons will engage progressively higher torque segments to maintain relatively constant ribbon tension. Such measures and the cost of frictional components that will last the life of the printer contribute significantly to the cost of the printer.

00006European Patent Application 0 408 356 A2 to Inoue teaches a ribbon supply core that is reversely rotated to prevent slack. However, the mechanism is reverse driven by the printer rather than operating on elastically stored energy, and it is connected to the printer frame rather than being part of a ribbon cartridge.

00007U.S. Pat. No. 5,284,396 to Masamura, et. al. teaches two embodiments of a ribbon supply spindle in which energy is stored in an extension spring or torsion spring. In the preferred embodiment, energy is stored in an extension spring and the resulting torque is transferred to a rotatable shaft on which a ribbon supply spool is fixedly mounted. In the alternate embodiment, the shaft is fixed and a ribbon supply spool is rotatably mounted and made nonremovable by a collar, which bears upon a clutch plate and torsion spring, which provides the stored energy. In both embodiments, however, the spring and clutch are part of the printer mechanism, and therefore require operator torque adjustment to accommodate a range of ribbon widths. Moreover, such components must be made of material suitable to the useful life of the printer rather than the useful life of the ribbon.

00008European Patent Application 0 165 396 to Kitagishi teaches a ribbon cassette with a constant tension imparting mechanism consisting of friction members that are compressed by a plate spring and which sandwich the ribbon. The spring provides frictional force rather than storing energy, and is “H-shaped” to specifically prevent it from doing so, thereby producing equal drag in both directions of ribbon movement. Thus, if the ribbon according to Kitagishi is advanced then released with slack, the slack will remain.

00009U.S. Pat. Nos. 6,126,344 and 5,788,387 and 5,595,447 to Takayama et al. teach a tape cartridge and printing device having an anti-slack mechanism for preventing slack of the ink ribbon through engagement of a ribbon winding core with an anti-rotational engagement piece. This mechanism, however is intentionally disengaged when the cartridge is set in the printing device rather than being intended to work during printing.

00010U.S. Pat. No. 4,838,716 to Shinada teaches a ribbon cartridge having a brake mechanism for preventing unnecessary rotation of the feeding ribbon roll. A spring is used to urge a takeup roller against a driven roller so as to pull ribbon from the supply. However, Shinada does not teach or suggest a mechanism to store energy in the supply cartridge or roll and retract slack ribbon into the cartridge or onto the roll.

SUMMARY OF THE INVENTION

00011The present invention provides a thermal transfer ribbon cartridge and alternatively a ribbon roll capable of supplying ribbon and maintaining a minimum ribbon tension by retracting a limited amount of ribbon slack. Further, in accordance with the present invention, there is provided a thermal transfer printer having passive support means for the cooperating ribbon cartridge in lieu of a ribbon spindle.

DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate preferred embodiments of the invention to facilitate a thorough understanding of it. The invention includes certain novel features and structural details hereinafter fully described and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.

<figref idref="DRAWINGS">FIG. 1</figref> is a side elevation view of a specific embodiment of thermal transfer printer provided by the present invention showing a transfer ribbon cartridge adapted to cooperate with the printer in advancing the transfer ribbon and maintaining constant ribbon tension.

<figref idref="DRAWINGS">FIG. 2</figref> is a perspective view of a specific embodiment of the cooperating ribbon cartridge according to the preferred embodiment.

<figref idref="DRAWINGS">FIGS. 3</figref><i>a </i>and <b>3</b><i>b </i>are sectional views of the cooperating ribbon cartridge according to the preferred embodiment.

<figref idref="DRAWINGS">FIGS. 4</figref><i>a </i>and <b>4</b><i>b </i>are sectional views of an alternate embodiment.

<figref idref="DRAWINGS">FIGS. 5</figref><i>a </i>and <b>5</b><i>b </i>are sectional views of an alternate embodiment.

<figref idref="DRAWINGS">FIG. 6</figref> is a perspective view of an alternate embodiment.

DETAILED DESCRIPTION

00019Referring to the drawings, <figref idref="DRAWINGS">FIG. 1</figref> is a pictorial representation of a thermal transfer printer <b>10</b>. Thermal transfer printer <b>10</b> includes a thermal print head <b>12</b> for printing images on a web <b>14</b>, such as a roll of pressure sensitive labels, tickets, or tags, by transferring ink from a transfer ribbon <b>16</b> to web <b>14</b> at print line <b>18</b>. Web <b>14</b> is advanced by a platen <b>20</b>, which carries transfer ribbon <b>16</b> along with it due to the frictional contact with web <b>14</b> at print line <b>18</b> under pressure of spring <b>15</b>. Platen <b>20</b> is driven by a stepper motor <b>22</b> through a belt <b>24</b> and a drive pulley <b>26</b>. After printing a label, ticket, or tag, web <b>14</b> is advanced to a cutting edge <b>28</b> where the label, ticket, or tag can be torn off by the user. The torn edge <b>30</b> is then retracted before printing the next label, ticket, or tag.

00020Spent transfer ribbon <b>32</b> passes from print line <b>18</b> via a guide <b>34</b> to a takeup core <b>36</b> removably positioned on a takeup spindle <b>38</b>. Takeup spindle <b>38</b> is driven by belt <b>24</b> through a pulley <b>40</b> and a clutch (not shown), which limits the takeup torque to avoid breaking the ribbon.

00021Transfer ribbon <b>16</b> is fed from ribbon roll <b>42</b>, which is wound on core <b>44</b> and contained within a ribbon cartridge <b>46</b>, passing around guide <b>47</b> to print line <b>18</b>. Thermal printer <b>10</b> is adapted to receive and support ribbon cartridge <b>46</b> on shelf <b>48</b>. Cartridge <b>46</b> includes certain novel features and structural details further illustrated in FIG. <b>2</b> and described below.

00022With reference to <figref idref="DRAWINGS">FIG. 2</figref>, cartridge <b>46</b> includes a carton <b>47</b>, preferably formed of cardboard or corrugated fiber-board, which encloses ribbon roll <b>42</b>, wound on hollow core <b>44</b>, and preferably formed of fiber or alternatively formed of plastic. Core <b>44</b> further encloses brake <b>48</b>, formed of an elastomer, preferably urethane. Slots <b>92</b> and <b>94</b> in facing walls of carton <b>47</b> capture the ends of brake <b>48</b> and prevent its rotation.

00023With reference to <figref idref="DRAWINGS">FIG. 3</figref><i>a</i>, brake <b>48</b> includes a clutch section <b>66</b>, spring sections <b>68</b> and <b>70</b>, and end sections <b>72</b> and <b>74</b>. Clutch section <b>66</b> is dimensioned for an interference fit with core <b>44</b>. The degree of interference and the durometer and thickness of brake <b>48</b> are chosen to define a desired drag torque on roll <b>42</b> at which core <b>44</b> will begin to slip against clutch section <b>66</b>. Note that although drawn as rectangular in cross section to facilitate understanding, brake <b>48</b> and the corresponding slots <b>92</b> and <b>94</b> (not shown) may be, for example, non-rectangular in cross section while remaining within the scope of the invention.

00024Spring sections <b>68</b> and <b>70</b> are typically of smaller cross section so as not to interfere with the rotation of core <b>44</b>, but rather to twist elastically as indicated in <figref idref="DRAWINGS">FIG. 3</figref><i>b</i>, thus permitting clutch section <b>66</b> to rotate until the drag torque is reached and clutch section <b>66</b> slips continuously against core <b>44</b> as ribbon <b>16</b> is withdrawn. The energy thus stored in spring sections <b>68</b> and <b>70</b> serve to retract slack when ribbon <b>16</b> is backfed. Depending on the characteristics of the elastomer, spring sections <b>68</b> and <b>70</b> may be, for example, notches or slits in brake <b>48</b>.

00025In the alternate embodiment of <figref idref="DRAWINGS">FIGS. 4</figref><i>a </i>and <b>4</b><i>b</i>, brake <b>48</b> is rotated ninety degrees and inserts <b>58</b> and <b>60</b>, preferably formed of thermoformed plastic, support the weight of roll <b>42</b> by means of protrusions <b>62</b> and <b>64</b> respectively protruding into core <b>44</b>. If present, such supports <b>58</b> and <b>60</b> include slots <b>59</b> and <b>61</b> (not shown) to capture the ends of brake <b>48</b>. Supports <b>58</b> and <b>60</b> may be used in addition to slots in the carton as previously described, or in the alternative.

00026It is intended that brake <b>48</b> not be limited to an elastomeric material in order to lie within the scope of the invention. According to the alternate embodiment of <figref idref="DRAWINGS">FIGS. 5</figref><i>a </i>and <b>5</b><i>b</i>, a multi-diametral (i.e., having more than one diameter) spring <b>76</b> has a clutch section <b>78</b> having an outer diameter chosen for an interference fit to core <b>44</b> and forming a spring clutch structure, and two torsion spring sections <b>80</b> and <b>82</b> of lesser diameter. Spring <b>76</b> is anchored to holes <b>84</b> and <b>86</b> (not shown) in inserts <b>88</b> and <b>90</b> that prevent its overall rotation. Alternatively, spring <b>76</b> may be anchored directly to holes in the facing walls of cartridge <b>46</b> in lieu of inserts at the loss of some ease of assembly.

00027According to the alternate embodiment of <figref idref="DRAWINGS">FIG. 6</figref>, brake <b>48</b> further includes axial hole <b>96</b>. Ribbon roll <b>42</b> is supported by a passive pin <b>98</b> fixed to printer <b>10</b>. Brake <b>48</b> is captured and prevented from rotating by slot <b>99</b>, also a part of printer <b>10</b>.

00028It should be noted that brake <b>48</b> or the equivalent multi-diametral spring <b>76</b> is not limited to a single structure to lie within the scope of the invention, and that either may equivalently be comprised of individual parts performing the spring and clutch functions.

00029It should also be noted that the conditions of interference fit or free motion between the sections of the brake and the ribbon core can equivalently be met with a multi-diametral ribbon core and a brake of uniform dimensions, and that such structures lie within the intended scope of the invention.

00030Further, it should be noted that the ribbon can be wound on a core longer than the ribbon width, or the core as described can be fitted to an internal spindle and the clutch functionality coupled to the outside diameter of the core or spindle rather than to the inside diameter. While such embodiments may be more costly to manufacture, it is intended that they fall within the scope of the invention.

00031Cartridge <b>46</b> is intended to be disposable, hence core <b>44</b>, and brake <b>48</b> or equivalently spring <b>76</b> can be dimensioned to provide the drag torque specific to the composition and width of ribbon <b>16</b>. This eliminates the ribbon supply torque mechanisms or user adjustments of the prior art thermal printers.

00032Specific embodiments of a thermal ribbon cartridge or roll according to the present invention have been described for the purpose of illustrating the manner in which the invention may be made and used. It should be understood that implementation of other variations and modifications of the invention and its various aspects will be apparent to those skilled in the art, and that the invention is not limited by the specific embodiments described. It is therefore contemplated to cover by the present invention any and all modifications, variations, or equivalents that fall within the true spirit and scope of the basic underlying principles disclosed and claimed herein.